1. Field of the Invention
The present invention relates to a method of decelerating projectiles. More specifically, the present invention relates to a method for improving the deceleration of projectiles with a rubber trap, and to improving stability of the rubber material.
2. State of the Art
In order to maintain proficiency in the use of firearms, it is common for law enforcement officers and sportsmen to engage in target practice. Target practice was traditionally conducted in settings where preventing ricochets was the primary concern, and the concern over recovery of bullets was secondary or nonexistent. Firing ranges commonly used a large mound of earth to decelerate the bullet after it had passed through the target. Such systems generally prevented injury from ricochets, etc, because the dirt was effective in stopping the bullets.
More recently, however, considerable concern has been raised about the lead contained in the bullet. Though the bullet fired in to the mound of dirt was safely contained from the point of being a moving projectile with a significant amount of inertial momentum, the lead in the bullet was free to leach into the environment. Thus, the more recent trend in shooting ranges has also stressed containment and removal of the bullet to prevent lead contamination of the environment.
In addition to the containment of lead bullets, there is also a desire to build shooting ranges within enclosed structures. For example, many police departments will have a shooting range within the police station. Having the range disposed inside is advantageous because it can be used frequently regardless of the weather and without undue travel time. However, in such ranges, mounds of dirt or similar materials are not generally practical.
The current trend in bullet containment systems has focused on two different types of systems. One kind of containment system, often called a bullet stop and containment chamber. Has a pair of plates which channel bullets toward an opening in a containment chamber. Inside the containment chamber are impact plates which slow the bullet to a stop. (As used herein, bullet includes bullets, shot and other forms of projectiles).
Bullet stop and containment chambers are highly advantageous because the entire deceleration process is controlled by sheets of steel plate. Such a system can withstand hundreds of thousands, if not millions, of rounds without showing excessive wear.
Unfortunately, bullet stop and containment systems which use steel plate containment chambers are also relatively expensive. Numerous sheets of the steel must be welded together to form the chambers. Transportation of the chambers and final construction of the systems can add considerably to cost. Furthermore, it is often difficult to construct such a system in a completed building which was not designed to receive the parts of the system.
Due to these difficulties, there has also been a significant increase in the number of lower-end bullet backstops being formed. Bullet backstops typically include a back wall plate made of steel. The back wall plate is usually disposed transverse to the ground at an angle of about 30-38 degrees. A plurality of support legs extend downwardly from the underside of the back wall plate to the ground.
On an upper side of the wall, a layer of impact material is disposed to provide a medium for decelerating bullets which is several feet thick along the plane the bullet travels. The impact material in such bullet traps has traditionally been dirt or sand. However, over the last decade there has been a trend toward the use of rubber pieces to decelerate the bullets. As a bullet impacts the pieces of rubber, it decelerates sufficiently that if it does impact the back wall plate, any ricocheting will be minimal.
U.S. Pat. No. 5,848,794 to Wojcinski et al (hereinafter xe2x80x9cthe ""794 patentxe2x80x9d), discloses an example of a rubber berm bullet trap. FIG. 1 shows a projectile trap assembly, generally indicated at 6 made in accordance with the ""794 patent. The trap assembly includes a support frame 10 having a front wall 14 and rear wall 16 supporting an inclined member 11. Supported by the upper surface 12 of inclined member 11 is a particulate flowable granulate material 30.
The upper surface 12 is inclined relative to the line of the projectiles, which typically is substantially parallel to ground. As illustrated, the upper surface 12 is inclined substantially at the angle of repose A of the particulate granulate material, thereby providing a constant depth of granulate material 30 over the entire upper surface 12 of inclined member 11. As shown in FIG. 1, the angle of repose is approximately 38 degrees.
To further facilitate entrapment of the projectiles and to prevent splashing of the granulate particles, projectile trap assembly 6 includes a self-healing member 44 covering the particulate granulate material 30, as illustrated in FIG. 1.
The granulate material 30 typically consists of pieces of rubber having an average size of about 5-7 mm in diameter. Rubber particles of this size provide a sufficiently dense medium to slow entering projectiles when the layer of granulate material is about 2 feet deep.
The ""794 patent further teaches the use of an anti-adhesion, fire retardant material to prevent adhesion between the granulate material 30 in the presence of heat and to prevent the rubber material from being ignited by rounds fired into the material.
The granulate material 30 recommended for the bullet trap 6 shown in FIG. 1, is configured to be easily flowable when it is applied to the inclined member 11. This flowability is an important aspect of the trap 6 of FIG. 1 to facilitate removal of the granulate material so that bullets contained therein can be removed and disposed of in accordance with environmental guidelines.
The touted advantages of the configuration discussed above provides countervailing disadvantages. Specifically, the granulate material remains flowable during use of the range. Firing rounds into the small pieces of rubber forming the granulate material 30 causes vibration and splashing. The vibrations and splashing, in turn, cause the granulate material to advance toward the bottom of the inclined member 11. Using the granulate material 30 without the self-healing member 44 can result in uneven layers of the granulate material and requires the floor in front of the trap to be cleaned frequently.
The use of granulate materials, such as the recommended 5-7 millimeters, also increases the risk that the granulate material will be ignited by a bullet fired into the trap 6. Bullets remain hot until after they have come to a complete rest. Because they have a larger effective surface area, smaller pieces of granulate material will potentially ignite more readily than larger pieces of the same material. Thus, a larger amount of fire retardant must be used to achieve the same result.
Thus, there is a need for an improved apparatus and method for bullet deceleration which provides all of the advantages of rubber bullet traps without the disadvantages of the currently available systems.
Thus, it is an object of the present invention to provide a bullet deceleration backstop which provides increased stability to the rubber material used to decelerate the bullets.
It is another object of the present invention to provide such a bullet deceleration trap in which the pieces of rubber tend to adhere to one another.
It is still yet another object of the present invention to provide such a bullet trap wherein the rubber material is mixed with a fire retardant material which inhibits ignition of the rubber without interfering with adhesion.
It is still yet another object of the present invention to provide such a bullet trap wherein an adhesive is applied to the rubber material to enhance adhesion between adjoining pieces of rubber.
The above and other objects of the invention are realized in specific illustrated embodiments of a bullet deceleration backstop including a deceleration material formed from a synthetic rubber, typically shredded automobile tires.
In accordance with one aspect of the invention, the rubber pieces or nuggets are preferably between 15 and 25 millimeters in diameter. The larger pieces of rubber provide several advantages. First, the rubber nuggets set forth in the present invention have approximately 25 to 100 times greater volume than the pieces of granulate material of the prior art. The increased mass associated with a rubber nugget provides greater stopping power for decelerating a bullet. Second, the larger material is less prone to sluffing and can be stacked at a greater incline without falling. Third, the larger nuggets of material are less prone to ignite from contact with hot metal.
In accordance with another object of the present invention, the rubber nuggets are covered with a fire retardant material. Unlike the prior art, the fire retardant material is selected to not interfere with adhesion between the pieces of rubber. As rounds are fired into the rubber, adjoining pieces are bonded together by the heat, thereby forming a larger rubber nugget.
Adhesion of the rubber nuggets provides several advantages. First, using larger pieces of rubber and having pieces of rubber adhered to one another provides for a more stable mound of rubber. The increased stability of the rubber material enables the mound to be formed at a greater incline without excessive sluffing of the material. This reduces clean-up and eliminates the need to cover the rubber pieces with a self-healing cover. Additionally, being able to place the material at a greater incline decreases the space which is consumed by the backstop. Thus, a shooting range can be contained in a smaller area while still providing an effective mechanism for decelerating the bullets.
Another advantage of allowing adhesion is that rubber material can be maintained for a longer period of time. When a round impacts a mound of rubber, some of the rubber pieces will be sheared or fractured into smaller pieces. By promoting adhesion between the smaller piece (preferably both in the presence of heat and the absence of heat), the pieces of rubber can be held together. More energy is consumed when the bullet impacts the clumps of rubber and the formation of new clumps by heat from the bullet prolongs the usefulness of the rubber nuggets as a bullet deceleration material.
In accordance with still another aspect of the invention, a glue added to the rubber nuggets. Preferably, the glue is sprayed on the pieces of rubber along with the fire retardant. As the glue dries, it holds the rubber nuggets together. This further facilitates stability of the rubber trap and improves bullet deceleration.
In accordance with another aspect of the invention, the glue is selected to have adhesive properties when it is moistened. Periodically spraying the rubber with water causes the glue to adhere the rubber pieces to one another and prolong the life of the rubber nuggets in the trap.